Evaporator arrangement for the coating of substrates

ABSTRACT

The invention relates to an evaporator arrangement with a crucible, wherein the crucible is divided into at least two zones, each of which is heated to different temperatures. The first zone is a melt-down zone and the second zone the evaporation zone proper. The evaporator arrangement is preferably for the evaporation of metals. If metals are evaporated, a metal wire is preferably guided into the melt-down zone. However, metal alloys can also be evaporated thereby that one or several metal wires comprised of different materials are guided into the melt-down zone. Between the melt-down zone and the evaporator zone a heating zone may be provided.

BACKGROUND AND SUMMARY OF THE INVENTION

This application claims priority from European Patent Application No: 050 16 832 filed Aug. 3, 2005, incorporated herein by reference in its entirety.

The invention relates to an evaporator arrangement for the coating of substrates with at least one material.

Apart from the electrolytic method, the coating of a substrate with a material can also take place by sputtering or by vapor deposition. The layer generated in this manner often serves for protecting the coated material; however, it may also have purely decorative or functional relevance.

Applying a layer by vapor deposition is of great importance especially in the coating of substrates with metals. In this method a metal is melted in a crucible with the temperature being selected such that the metal changes to the gaseous state and migrates in the direction of the substrate to be coated, where it condenses.

For coating substrates evaporator units are known in which several evaporator boats are disposed in an evacuated space. Into these evaporator boats is introduced, frequently in a continuous process, material in the form of a wire which is evaporated. This vapor rises and condenses on the substrate to be coated, and the substrate, often in the form of a band, is guided over the evaporator boats. Of disadvantage in this evaporator unit is that splatters are generated during the direct evaporation, since irregular vapor pressures are formed due to impurities and gaseous components. The splatters are moreover formed by rapid movement of the melt in hot zones of the evaporator boats. In addition, the melting off of the wire, which to some extent is discontinuous, leads to different evaporation rates since these are dependent on the target site of the wire.

DE 40 27 034 C1 discloses an evaporator arrangement for coating band-shaped substrates in a vacuum coating chamber. The evaporator boats utilized in this case form an evaporator bank, the boats being disposed longitudinally with respect to the running direction of the band and parallel and approximately equidistantly with respect to one another.

Furthermore is known from DE 44 04 550 C2 an arrangement for the regulation of the evaporation rate from crucibles heated by current throughflow, wherein metal is evaporated in these crucibles. In this case the regulation of the evaporation rate takes place via an electrical resistance heating system, the total resistance resulting from the electrical resistance of the crucible and from the electrical resistance of the material in the crucible.

An arrangement for the evaporation of metal is furthermore known, wherein a wire is inserted into a groove which is in flow connection with an evaporator crucible (DE 34 28 651 A1). Due to the different vapor pressures, impurities and gaseous components can lead during the melting of the wire to the generation of splatters, which reach the substrate. To avoid this, above the groove a cooled screening or cover is disposed. This ensures that the substrate is only coated by the material rising from the evaporator crucible.

Furthermore, other evaporator boats are also known, in which between a first zone and a second zone a screening in the form of a wall is located. This wall is intended to prevent splatters generated during the melting of the metal from reaching the substrate to be coated (U.S. Pat. No. 3,467,058, EP0 430 210 B1).

Lastly is also known another evaporator arrangement which comprises a melt-down zone, an evaporator zone and a connection between the two zones (U.S. Pat. No. 3,020,177 A; EP 1 327 699 A).

The problem underlying the invention comprises providing an evaporator arrangement for coating substrates with materials, in particular with metals, which is conceptualized such that no splatters can reach the substrate, wherein the installation of walls or other screenings is not necessary.

This problem is resolved according to the present invention.

The invention therewith relates to an evaporator arrangement with a crucible, wherein the crucible is divided into at least three zones, each of which is heated to different temperatures. The first zone is a melt-down zone and the second zone the heating zone and the third zone the evaporator zone. The evaporator arrangement is preferably suitable for the evaporation of metals. If metals are evaporated, a metal wire is preferably guided into the melt-down zone. However, metal alloys can also be evaporated thereby that one or several metal wires comprised of different materials are introduced into the melt-down zone.

The advantage attained with the invention consists in particular therein that a splatter-free and highly uniform evaporation rate is achieved for qualitatively high-grade layers on organic substrates, for example OLEDs, and synthetic films. This is of importance for example in the production of capacitors, where splatter-free layers must be applied onto extremely thin films with good uniformity and under low radiative loading. It is also advantageous that no high demands must be made of the precision of the wire guidance, since the target point of the wire on the heated crucible is unimportant to the evaporation rate. Since in the melt-down zone lower temperatures obtain than in the evaporator zone, the wire guidance is also under low thermal loading and low vapor deposits. Through the division into melt-down and evaporator zone, impurities such as grime or oxide layers can largely be kept away from the evaporator zone. The service life of the crucible is also increased since the liquid material to be evaporated only moves slowly.

Embodiments of the invention are shown in the drawing and will be explained in further detail in the following.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a perspective view of an evaporator arrangement with three zones,

FIG. 2 is a perspective view of a variant of the arrangement depicted in FIG. 1, each of the three zones having a separate heater,

FIG. 3 is a top view onto the evaporator arrangement according to FIG. 2,

FIG. 4 is a section of the evaporator arrangement according to FIG. 3 along A-A,

FIG. 5 is a section through another embodiment of the evaporator arrangement,

FIG. 6 is an evaporator bank with several evaporator boats.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of an evaporator arrangement 1 with a crucible 6 comprised of three zones. Into the first zone 2, the so-called melt-down zone, the material to be evaporated is introduced where it is melted. If the material is a metal, it can be introduced in the form of a wire 3 into the melt-down zone 2.

The wire 3 can be, as for example in U.S. Pat. No. 3,467,058, on a spool, from which it is continuously introduced into the melt-down zone 2. If an alloy is to be applied onto the substrate, the wire 3 can already be comprised of this alloy or the alloy can be produced by the simultaneous melting of several wires of the desired metals which are to form the alloy.

The manner in which the wire 3 is introduced into the melt-down zone 2 is insignificant, since no high demands are made of the precision of the wire guidance.

With this evaporator arrangement 1 such metals, or their alloys, are preferably to be evaporated which comprise Ag, Cu or Al.

The melt-down zone 2 of the crucible 6 is followed by a so-called heating zone 4, where a temperature obtains which must not reach the boiling temperature of the metal having the lowest boiling point, but which is higher than the temperature of the melt-down zone 2. In this heating zone 4 low boiling impurities are removed such that metals are obtained which have a very high degree of purity.

The heating zone 4 of crucible 6 has a form adapted to the material of the melt 25 and the particular temperature-dependent surface tensions. It often has the form of a channel, as shown here, which connects the melt-down zone 2 with an evaporator zone 5. The heating zone 4 is smaller than the zones 2 and 5 and prevents the interchange of the melt 25 in zones 2 and 5, since it is important that the colder region 2 is separated from the hotter region 5, for it is to be avoided that evaporation occurs already in the melt-down zone 2. The size of the heating zone 4 is a function of the material; it may in practice have a length of, for example, 10 mm. The temperature of the melt 25 increases continuously from zone 2 to zone 5.

When the melt 25 has passed through the heating zone 4 of the crucible 6, it reaches the evaporator zone 5, where the material is lastly vapor deposited onto the substrate, which is disposed over the evaporator zone 5.

The melting point of the material of the crucible 6 must be far above the evaporation temperature of the metals which are to be evaporated. Possible materials for the crucible 6 are high-melting compounds, and the crucible 6 can also be comprised of several compounds of this type. Apart from graphite, compounds of the metallic borides, nitrides or carbides for example can be utilized as well as compounds of the non-metallic borides, nitrides or carbides. TiB₂ together with BN are suitable as materials of the crucible 6.

The crucible 6 is heated in such manner that the temperature in region 2 is lowest and in region 5 highest, wherein the heating can take place via only one or via several heaters operated separately of one another.

In the embodiment example shown in FIG. 1 the heating takes place through a current which flows through the crucible 6, and specifically in its longitudinal direction. For this purpose a voltage source 28 is connected via lines 29, 30 to the ends of the crucible 6. Due to the recesses 31 to 38 at the sides of the crucible 6 different electrical resistances result at the different zones. At those zones at which the crucible 6 is very narrow, high electrical resistance results and therewith a high temperature, since according to the formula W=R*I² this temperature is proportional to the electrical resistance, where W=electric power, R=resistance and I=electric current. Since the electric power is proportional to the temperature, consequently a relation between the cross sectional width of crucible 6 and the temperature obtaining there results. It now becomes feasible to calculate the form of the crucible 6 such that at specific sites specific temperatures are attained for example of 1200° C. in the melt-down zone 2, of 1260° C. to 1496° C. in the heating zone 4 and of 1560° C. in the evaporator zone 5. The particular temperatures are however dependent on the particular material to be evaporated. Consequently, the geometry of the crucible 6 may differ from material to material.

For aluminum applies for example that the temperature in the melt-down zone 2 is higher by approximately 300 to 500° C. than the melting point and in the evaporator zone 5 higher by approximately 900° C. The temperatures in zones 2 to 4 are selected such that in them no evaporation of the material occurs. It would theoretically be sufficient for the temperature in the melt-down zone to be only marginally above the melting temperature. However, since the introduced metal wire leads to a cooling down, the temperature in the melt-down zone is selected higher.

It is understood that the resistance relationships can be obtained not only through lateral indentations but also through different thicknesses of the crucible material in the vertical direction. Significant is the particular total cross section which is accountable for the electrical resistance.

The rising vapor lobe of the metal to be evaporated remains nearly constant during the evaporation, whereby the coating becomes highly uniform. If several evaporator boats form an evaporator bank, the evaporator boats are oriented such that the substrate is uniformly coated. This can be achieved not only through the disposition of the evaporator boats with respect to one another, but also thereby that the substrate is guided over the evaporator bank at such distance that uniform coating results.

By separating the evaporator zone 5 from the melt-down zone 2 the movement of liquid metal in the evaporator zone 5 itself is very low whereby the service life of the evaporator arrangement 1 is also increased.

The evaporation rate can be controlled via the speed of the melting-down of the wire and the geometry of the crucible 6. For continuous operation of the evaporator arrangement 1 regulation of the level of fill of the melt 25, of the wire advance and of the evaporator output can be provided.

Since the evaporation rate is highly uniform and no splattering occurs which may reach the substrate, such an evaporator arrangement 1 is suitable for the coating of, for example, synthetic films with metal. The evaporation rate is therein determined via the surface of the evaporator zone 5, the temperature of the evaporator crucible as well as the wire feed, i.e. the quantity of molten wire 3 per unit time. Such an arrangement can for example be utilized for the fabrication of capacitors, since here splatter-free layers are applied onto extremely thin films and the layers, moreover, must be highly uniform.

A further application field is also the production of metallic yarn, since here the requirements made of the evaporator arrangement 1 are also very high.

FIG. 2 shows a perspective view of a variant of the evaporator arrangement 1 shown in FIG. 1. The melt-down zone 2, the heating zone 4 and the evaporator zone 5 of the crucible 6 have each their own electrical resistance heater 21, 22, 23. Therewith the three zones can be brought to different temperatures. Between the individual zones 2, 4 and 4, 5, respectively, are located insulating layers 39 to 42, such that the currents clearly flow in the transverse direction. The DC voltage sources 18 are in this case all at their own resistance, to which they can be connected via switches 19. Instead of constant DC voltage sources 18, regulatable DC voltage sources can also be employed. In addition, AC voltage sources can be utilized.

Instead of three separate voltage sources 18, it is also feasible to provide only one voltage source, parallel with which the three zones 2, 4, 5 are connected. In order to generate here different temperatures in different zones, the zones may be comprised of different materials or have different current flow cross sections.

FIG. 3 shows a top view onto the evaporator arrangement 1 depicted in FIG. 2. Evident is that the wire 3 is introduced obliquely from above into the melt-down zone 2, where the metal or the alloy melts. This melt 25 migrates via the heating zone 4 into the evaporator zone 5, where lastly evaporation occurs. Clearly visible is the heating zone 4 narrowing toward the evaporator zone 5, which is implemented as a channel. This channel is formed in a manner as is required by the molten material and its temperature-dependent surface tension.

FIG. 4 shows a section along A-A in FIG. 3. The wire 3 is brought into the melt-down zone 2, which is connected via the heating zone 4 with the evaporator zone 5. The basin 24 of the melt-down zone 2 is deeper than the basin 26 of the evaporator zone 5. Since the bottom of the heating zone 4 is above the bottom of the melt-down zone 2, the molten metal can only flow into the evaporator zone 5 if sufficient metal has been melted from the wire in order to reach the level which corresponds at least to the height of the heating zone 4. The bottom of basin 26 of the evaporator zone 5 lies below the bottom of the heating zone 4.

The basins of the different zones can however all be at the same level or only the basins of zones 4 and 5 can lie at the same level. A flow of the material from the melt-down zone 2 to the evaporator zone 5 takes place in this case also since the level of the material in the evaporator zone 5 decreases due to the evaporation and therewith draws material from the melt-down zone 2.

FIG. 5 shows a variant of the arrangement depicted in FIG. 4. In contrast to the evaporator arrangement depicted in FIG. 4, the heating zone 4 has a gradient toward the evaporator zone 5.

In FIG. 6 is shown the manner in which several crucibles or evaporator boats 45 to 54 can be disposed in a coating unit. Each evaporator boat 45 to 54 is therein fed with its own wire 55 to 64, and specifically via, not shown, wire supplies. The substrate to be coated is here a film 65, which is guided past via a coating roller 66 in the evaporator boats. The direction of movement of the film 65 corresponds therein to the longitudinal direction of the evaporator boats. The three zones of the evaporator boats 45 to 54 are not shown in FIG. 6.

The evaporator boats 45 to 54 are disposed on an evaporator bank 67, which can be slid under the coating roller 66. However, it is also conceivable that the evaporator boats 45 to 54 are disposed on a slide-in cart, which can also be slid under a coating roller.

In FIG. 6 all evaporator boats 45 to 54 are open, i.e. no regions of them are covered.

However, it is also feasible to dispose above the evaporator zone 5 of the crucible according to FIG. 1 a distributor tube perpendicularly above the evaporator zone 5, this distributor tube comprising numerous throughbores linearly disposed in the vertical direction, via which the vapor is directed onto a substrate. Such a distributor tube is known for example from DE 102 56 038 A1.

Instead of electrical resistance heaters, inductive heaters can also be provided, which are so laid out such that they generate different temperatures in different zones of an evaporator boat. 

1-20. (canceled)
 21. An evaporator arrangement for the coating of a substrate with at least one material, comprising at least one crucible having a) a melt-down zone, b) an evaporator zone, c) a connection between the melt-down zone and the evaporator zone, d) a heating device which permits heating each of the melt-down zone and the evaporator zone to different temperatures, wherein the connection between the melt-down zone and evaporator zone is a heating zone with a basin open at the top, via the surface of which a molten material flows from the melt-down zone into the evaporator zone, wherein the temperature of the heating zone lies between the temperature of the melt-down zone and the temperature of the evaporator zone.
 22. An evaporator arrangement as claimed in claim 21, wherein the crucible is electrically conducting and the heating device is formed by a voltage source in connection with the geometry and the material of the crucible, wherein the voltage source is in contact on the ends of the crucible.
 23. An evaporator arrangement as claimed in claim 21, wherein the melt-down zone, the heating zone and the evaporator zone of the crucible are separated from one another by insulating layers and to each zone one voltage source is assigned.
 24. An evaporator arrangement as claimed in claim 21, wherein the heating of the zones to different temperatures takes place by means of inductive heating.
 25. An evaporator arrangement as claimed in claim 21, wherein the temperature in the heating zone increases continuously from the melt-down zone in the direction toward the evaporator zone.
 26. An evaporator arrangement as claimed in claim 21, wherein the zones are formed by different geometric cross sections of the crucible, whereby the electrical resistance in the zones varies.
 27. An evaporator arrangement as claimed in claim 21, wherein the zones are comprised of materials of different electrical conductivity.
 28. An evaporator arrangement as claimed in claim 21, wherein the heating zone is developed similarly to a channel.
 29. An evaporator arrangement as claimed in claim 21, wherein the melt-down zone and the evaporator zone are in the shape of a cylindrical pot.
 30. An evaporator arrangement as claimed in claim 21, wherein the deepest sites of the zones are at different levels.
 31. An evaporator arrangement as claimed in claim 21, wherein the deepest sites of the zones are at the same level.
 32. An evaporator arrangement as claimed in claim 21, wherein the deepest site of the heating zone is at a higher level than the deepest sites of the melt-down zone and of the evaporator zone.
 33. An evaporator arrangement as claimed in claim 32, wherein the heating zone has a gradient in the direction toward the evaporator zone.
 34. An evaporator arrangement as claimed in claim 21, wherein the melt-down zone and the evaporator zone have a rectangular base.
 35. An evaporator arrangement as claimed in claim 21, wherein the melt-down zone and the evaporator zone have a circular base.
 36. An evaporator arrangement as claimed in claim 21, wherein the crucible is comprised of a high-melting compound selected from the group consisting of a metallic boride, a metallic nitride, a metallic carbide, a nonmetallic boride, a nonmetallic nitride, a nonmetallic carbide graphite, or a mixture thereof.
 37. An evaporator arrangement as claimed in claim 36, wherein the crucible comprises at least one of TiB₂ and BN.
 38. An evaporator arrangement as claimed in claim 21, wherein a plurality crucibles are disposed one next to the other.
 39. An evaporator arrangement as claimed in claim 39, wherein for each crucible a separate supply for a wire is provided, wherein the end of this wire is guided into the melt-down zone of a crucible.
 40. A method comprising coating a substrate with an evaporator arrangement of claim
 21. 41. The method of claim 40, wherein metals are evaporated.
 42. The method comprising coating a substrate with the evaporator arrangement of claim 38, wherein a substrate is moved along the longitudinal axis of the crucibles. 